a(n) = n! * Sum_{k=0..n} k^(3*n)/k!.A356688a(n) = n! * Sum_{k=0..n} k^(3*n)/k!.Terms a(0) =1a(1) =1a(2) =66a(3) =21225a(4) =18952156a(5) =36175231585External referencesoeis: A356688